This invention relates to a low-noise choked waveguide, and more particularly to an assembly that has low noise characteristics and low heat transfer for supporting a waveguide through cryogenically cooled space.
In microwave systems, it is often necessary to couple a waveguide that is at ambient temperature (300.degree. K.) to some cryogenically cooled device, such as a parametric amplifier at 70.degree. K., or a maser at 4.degree. K. This requires a cooled waveguide, but since the waveguide itself is a good thermal conductor, leakage and interference is experienced, thus degrading the sensitivity of such low-noise microwave amplifiers. In the past, a choked waveguide has been thermally spaced from a mounting plate at ambient temperature by spacers made of a material that exhibits very low thermal conductivity. That arrangement has been found to contribute 3.degree. to 3.5.degree. K. noise. It would be desirable to reduce this noise contribution by an order of magnitude to about 0.32.degree. K.